异化铁还原菌介导的硝酸盐还原亚铁氧化过程

Nitrate-reducing Fe(Ⅱ)oxidation mediated by dissimilatory iron-reducing bacteria

中性厌氧的富铁环境中,微生物驱动硝酸盐还原亚铁氧化(NRFO)过程和异化铁还原过程,然而异化铁还原菌能否介导NRFO仍未知。选取异化铁还原菌(Klebsiella pneumoniae L17、Shewanella oneidensis MR-1、Shewanella putrefaciens strain CN32)、亚铁和硝酸盐,构建厌氧NRFO体系。结果表明:亚铁氧化、硝酸盐还原同步发生,主要是因为硝酸盐还原产物亚硝酸盐可以直接氧化亚铁;亚铁抑制了硝酸盐还原,且该抑制作用随亚铁浓度升高而增强;亚铁对亚硝酸盐的竞争性还原导致了铵根大量减少;亚铁氧化生成的次生矿物沉淀在细胞表面,阻碍硝酸盐进入细胞进行还原。在低浓度亚铁条件下,亚铁的毒害和氧化成矿作用抑制L17还原硝酸盐;亚铁氧化成矿作用是抑制CN32还原硝酸盐的主要原因;而亚铁的毒害是抑制MR-1还原硝酸盐的主要原因。在高浓度亚铁条件下,亚铁氧化导致细胞结壳是抑制微生物硝酸盐还原的主要原因。

Microbially-mediated nitrate-reducing Fe(Ⅱ)oxidation(NRFO)process and alienated iron reduction process are ubiquitous under neutral anaerobic iron-rich environments.However,it is still unknown whether NRFO can be mediated by dissimilatory iron reducing bacteria.In this study,anaerobic NRFO system is constructed by selecting dissimilatory iron-reducing bacteria(Klebsiella pneumoniae L17,Shewanella oneidensis MR-1,and Shewanella putrefaciens strain CN32),ferrous and nitrate.The results show that nitrate reduction and Fe(Ⅱ)oxidation occurred simultaneously.The intermediate product nitrite during nitrate reduction is considered the dominant contributor to the overall Fe(Ⅱ)oxidation.The presence of Fe(Ⅱ)inhibited microbial nitrate reduction,and the inhibitory effect of Fe(Ⅱ)was more significant with the higher Fe(Ⅱ)concentration.Competitive reduction of nitrite by Fe(Ⅱ)resulted in the decrease of ammonium production.Fe(Ⅱ)oxidized secondary minerals precipitated on the cell surface,hindering nitrate from entering the cell for reduction.The toxicity and oxidation-mineralization of Fe(Ⅱ)inhibited nitrate reduction by L17 with low Fe(Ⅱ)concentration.Nitrate reduction by CN32 was inhibited by Fe(Ⅱ)oxidation-mineralization,while the inhibition of nitrate reduction by MR-1 was attributed to toxicity of Fe(Ⅱ).Under high Fe(Ⅱ)concentration,microbial nitrate reduction was inhibited by cell encrustation.